Lubricant

ABSTRACT

A lubricant in the form of lubricating oil or grease, for use in contact with graphite or molybdenum disulfide or in contact with aluminum materials, which comprises a perfluoropolyether oil free from (CF 2 O) n  groups as a repeat unit of polymer and having a kinetic viscosity at 40° C. of 50-1,500 mm 2 /sec., as a base oil, where F(CF 2 CF 2 CF 2 O) m C 2 F 5  or RfO[CF(CF 3 )CF 2 O] p (CF 2 CF 2 O) q Rf′ s used as the perfluoropolyether base oil. The lubricant undergoes no considerable deterioration of high-temperature characteristics (high-temperature durability), even if used in various uses as mentioned above, and also has distinguished low-temperature characteristics when the base oil has a kinetic viscosity of 50-250 mm 2 /sec.

TECHNICAL FIELD

The present invention relates to a lubricant, and more particularly to alubricant comprising a lubricating oil or a grease for use in contactwith graphite or molybdenum disulfide such as sintered, oil-impregnatedbearings containing graphite or molybdenum disulfide or for use incontact with aluminum materials such as sliding members, etc., formedfrom aluminum materials.

BACKGROUND ART

Sintered, oil-impregnated bearings comprises porous bodies madecompression of several kinds of solid powder obtained by adding solidlubricants such as graphite, molybdenum disulfide, carbon black, etc. tometal powders such as iron, copper, tin, zinc, etc. The sintered,oil-impregnated bearings can be used without any addition of oil owingto the self-lubrication action of a small amount of initiallyimpregnated lubricant. Thus, it is important for the life of bearingsthat the a sufficient amount of lubricant can be retained in thebearings and can be stably used for a long time.

Cheaper sintered, oil-impregnated bearings than the ball-and-rollerbearings have been increasingly used as automobile bearings, andconsequently the lubricant for use in such sintered, oil-impregnatedbearings have been inevitably exposed to such situations more strictwhere the high-temperature durability and low-temperaturecharacteristics of lubricant are essentially required. Lubricating oilcompositions comprising a perfluoropolyether oil as a base oil have beenso far used in such situations, and have been inevitably brought intoand kept with contact with some kinds of metals or solid lubricantshaving a very large surface area, so even the perfluoropolyether oilsfail to maintain stable high-temperature characteristics, depending ontheir structures.

Patent Literature 1: JP-B-2,595,583

Aluminum has a high specific strength in spite of its low specificgravity, and can have a higher strength upon alloying or processing andfurther has a corrosion resistance. Thus, the aluminum has been used invarious fields covering automobile parts, airplane and marine vesselparts, domestic electric appliances, electric tools, etc., of course,including sliding members, contributing to lighter weight of themachinery, higher working efficiency of high-speed revolution parts orsliding parts, or even to energy consumption saving. It is required thatlubricants for use even in the parts of aluminum materials must be ableto maintain their distinguished performance stably for a long time.

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

The present inventors have found that the high-temperaturecharacteristics of perfluoropolyether oil are drastically deterioratednot only due to the structure of perfluoropolyether oil, but also due tocontact with graphite or molybdenum disulfide used as one component ofthe sintered, oil-impregnated bearings, and further have found that theperfluoropolyether oil also undergoes drastic deterioration of thehigh-temperature characteristics even by contact of aluminum materials.

An object of the present invention is to provide a lubricant free fromconsiderable deterioration of high-temperature characteristics(high-temperature durability), when used in contact with graphite ormolybdenum disulfide such as sintered, oil-impregnated bearings, etc.containing graphite or molybdenum disulfide, or in contact with metallicparts such as ball bearings, etc. containing graphite or molybdenumdisulfide, or even used in contact with aluminum materials includingaluminum material as sliding members.

Means for Solving the Problem

Such an object of the present invention can be attained by a lubricantfor use in contact with graphite or molybdenum disulfide, or in contactwith aluminum materials, which comprises a perfluoropolyether oil freefrom (CF₂O)_(n) groups as a repeat unit of polymer and having akinematic viscosity at 40° C. of 50-1,500 mm²/sec., preferably 50-250mm²/sec., more preferably 65-200 mm²/sec., as a base oil. The lubricantmay be in any form of lubricating oil or grease, whereperfluoropolyether oils represented by the following general formulaecan be used as a base oil:

F(CF₂CF₂CF₂O)_(m)C₂F₅

RfO[CF(CF₃)CF₂O]_(p)(CF₂CF₂O)_(q)Rf′

EFFECT OF THE INVENTION

Perfluoropolyether oils undergo dramatically deterioration of thehigh-temperature characteristics (high-temperature durability) not onlydue to the structure of perfluoropolyether oils, but also due to contactwith graphite or molybdenum disulfide used as one component in thesintered, oil-impregnated bearings. The present invention provides alubricant free from considerable deterioration of high-temperaturecharacteristics when used in contact with graphite or molybdenumdisulfide such as the sintered, oil-impregnated bearings, etc.containing graphite or molybdenum disulfide, or in contact with metallicparts such as ball bearings, etc. containing graphite or molybdenumdisulfide. Cases of the lubricant as used in contact with metallic partsinclude those used in atmospheres where the graphite or molybdenumdisulfide prevails as scattered particles or as contaminants, forexample, cases in contact with graphite or molybdenum disulfide comingfrom motor parts such as brushes, shafts, etc. The atmospheres where thegraphite or molybdenum disulfide prevails as scattered particles or ascontaminants are not to be restricted to the afore-mentioned cases.

The perfluoropolyether oils having a kinematic viscosity at 40° C. of50-1,500 mm²/sec. can maintain the volatility and stability for a longtime, even if used at higher temperature more than 150° C. in thepresence of a solid lubricant such as graphite, molybdenum disulfide,etc., thereby attaining a longer life of parts to be used. Particularly,perfluoropolyether oils having a kinematic viscosity of 50-250 mm²/sec.,preferably 65-200 mm²/sec., have distinguished low-temperaturecharacteristics as well.

The present lubricant can be used in any mode of sliding includingrevolution, reciprocation, slipping, and oscillation, for example, assintered, oil-impregnated bearing or bushes containing graphite ormolybdenum disulfide in automobile uses fuel injectors including unitsfor controlling rates of idle revolution, units for recycling an exhaustgas, units for electronic throttle controlling, etc., and uses such asthose requiring a heat resistance, a low-temperature resistance and aload resistance, typically hub units, traction motors, alternators, etc.or in those requiring abrasion resistance or a low frictioncharacteristics, typically power transmission units, power wind motors,wipers, etc.; in information system uses requiring a high speed, a lowfriction coefficient, a low outgassing capacity, etc., typically harddisc drives, flexible disc memory devices, compact disc drives,photomagnetic disc drives, etc.; business machine uses, typically LBPscanner motors, etc.; and motor uses such as domestic electricappliances, sound equipment, etc., used in the high-temperaturecircumstances, etc. The present lubricant can be also effectively usedin atmospheres where graphite or molybdenum disulfide comes into contactwith the lubricant directly or through the contaminant prevailing there.

The high-temperature characteristics (high-temperature durability) ofperfluoropolyether oils are drastically lowered also when used incontact with aluminum materials including aluminum material as slidingmembers, but the present lubricant never undergoes considerabledeterioration of high-temperature characteristics, even when used insuch a case as above. That is, the present lubricant can maintain thevolatility or stability for a long time and can show a lubricability invarious sliding operations, even if used in the presence of aluminummaterials at higher temperature more than 150° C. or 200° C., therebyattaining an extremely longer life of parts to be used.

Besides such various uses as mentioned above, the present lubricant canbe used also in bearings or bushes of heated rolls used inplastics-processing machines, business machines, and copiers, and thoseof chains, etc. used in construction machines, machine tools,electrically driven tools, machines for printing, book-binding and paperprocessing, or their parts, and also can be used in lubrication ofcontacts between sliding members of ball-and-roller bearings, plainbearings, sintered bearings, gears, valves, cocks, oil seals, rolls,electric contacts, etc.

BRIEF DESCRIPTION OF DRAWING

[FIG. 1] A graph showing changes in percent weight loss with time ofvarious perfluoropolyether base oils in the presence of graphite ormolybdenum disulfide at 200° C.

BEST MODES FOR CARRYING OUT THE INVENTION

Base oils for use in the present invention are those having a kineticviscosity at 40° C. (according to JIS K2283, corresponding to ASTM D445)of 50-1,500 mm²/sec., preferably 50-250 mm²/sec., more particularly65-200 mm²/sec., and free from (CF₂O)_(n) groups as a repeat unit ofpolymer. As shown in the following Example 1 and FIG. 1 graph,determination of change with time (percent weight loss) ofperfluoropolyether oils allowed to stand in a thermostat tank at 200° C.reveals that changes with time of perfluoropolyol ether oil having(CF₂O)_(n) groups as a repeat unit of polymer are not particularlyconsiderable in the absence of graphite or molybdenum disulfide, ascompared with other perfluoropolyether oils, but are very considerablein the presence of graphite or molybdenum disulfide, whereas those freefrom (CF₂O)_(n) groups as a repeat unit of polymer have a slight changein such characteristic tendency even in the presence of graphite ormolybdenum disulfide, and thus perfluoropolyether oils free from(CF₂O)_(n) groups as a repeat unit of polymer can be selected as a baseoil for the present invention.

As shown in the results of the following Example 2, percent weight lossof the present lubricant at such a high temperature as 250° C. even inthe presence of aluminum materials is within an allowable range, andhave the similar tendency even at a the kinetic viscosity at −40° C.

Perfluoropolyether oils (base oil) free from (CF₂O)_(n) groups as arepeat unit of polymer includes the following perfluoropolyether oils:

F(CF₂CF₂CF₂O)_(m)C₂F₅  (A)

RfO[CF(CF₃)CF₂O]_(p)(CF₂CF₂O)_(q)Rf′  (B)

Perfluoropolyether oil (A): obtainable by anionic polymerization of2,2,3,3-tetrafluorooxetane in the presence of a cesium fluoridecatalyst, followed by a fluorine gas treatment of the resultingfluorine-containing polyether (CH₂CF₂CF₂O)_(n) under ultravioletirradiation at 160°-300° C. The product oils having a kinetic viscosityat 40° C. of 5-2,000 mm²/sec. are available, which can satisfyconditions of m=2-100 in the general formula for perfluoropolyether oil(A).

Perfluoropolyether oil (B): obtainable by complete fluorination of aprecursor formed by photooxidation polymerization of hexafluoropropyleneor together with tetrafluoroethylene, or by anionic polymerization ofhexafluoropropylene oxide or together with tetrafluoroethylene oxide inthe presence of a cesium fluoride catalyst, followed by a fluorine gastreatment of the resulting acid fluoride compound having the terminalCF(CF₃)COF groups. The product oils having a kinetic viscosity at 40° C.of 5-2,000 mm²/sec. are available, which can satisfy conditions ofp+q=2-200 and q/p=0-2:1 in the general formula for perfluoropolyetheroil (B).

When the kinetic viscosity is below 50 mm²/sec., the percent evaporationloss (percent weight loss) will be larger, and the oil film strengthwill be lowered, making the life shorter or causing attrition orseizure, whereas when the kinetic viscosity is above 1500 mm²/sec., thepour point will be much higher, resulting in not only a failure toobtain satisfactory low-temperature characteristics, but also theinconvenience of increasing a viscous resistance, thereby increasing apower consumption or a torque. So long as the base oil has a kineticviscosity at 40° C. of 50-1,500 mm²/sec., a satisfactory stability toheat resistance can be obtained. Particularly when good low-temperaturecharacteristics are required at a low temperature, for example, at −40°C., perfluoropolyether oil having a limited kinetic viscosity to 50-250mm²/sec., preferably 65-200 mm²/sec., can be used. Theperfluoropolyether oil having such a limited kinetic viscosity can notonly satisfy the evaporation loss-resisting characteristics orlow-temperature characteristics fully, but can be also used stably athigh temperatures over 200° C. A mixture of two or moreperfluoropolyether oils can be used, where the kinetic viscosity of sucha mixture of base oils must be within such a range as mentioned above.

A thickener, preferably fluororesin, can be added to the base oil. Thefluororesin for use herein includes, for example,polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropenecopolymer, perfluoroalkylene resin, etc. so far used as a lubricant.Polytetrafluoroethylene for use herein is such one as prepared byemulsion polymerization, suspension polymerization, solutionpolymerization, etc. of tetrafluoroethylene, thereby obtainingpolytetrafluoroethylene having a number average molecular weight Mn ofabout 1,000 to about 1,000,000, followed by heat decomposition, electronbeam-irradiated decomposition, physical pulverization, etc. thereof,thereby reducing the number average molecular weight Mn to about 1,000to about 500,000. Copolymerization of tetrafluoroethylene andhexafluoropropene, and successive treatment to reduce the molecularweight to a lower one can be carried out in the same manner as in thecase of polytetrafluoroethylene as mentioned above, and the resultingcopolymer having a number average molecular weight Mn of about 1,000 toabout 600,000 can be used. Molecular weight can be also controlled byusing a chain transfer agent at the time of copolymerization reaction.Powdery fluororesins thus obtained have an average primary particle sizeof generally not more than about 500 μm, preferably about 0.1 to about30 μm. Addition of powdery fluororesin can give the lubricant an oilfilm formability, anti-scattering and anti-leakage properties, and arust inhibitiveness, thereby making the lubricability and durabilitymuch better.

Other thickeners for use herein than the fluororesins include, forexample, metal soaps such as Li soap, etc., urea resin, minerals such asbentonite, etc., organic pigments, polyethylene, polypropylene,polyamide, etc., but from the viewpoint of heat resistance andlubricability it is preferable to use aliphatic dicarboxylic acid metalsalts, monoamide mono-carboxylic acid metal salts, monoester carboxylicacid metal salts, diurea, triurea, tetraurea, etc.

The thickener such as the powdery fluororesins, etc., can be used asadmixed in a proportion of 0.1-40% by weight, preferably 0.5-30% byweight, on the basis of total weight of composition comprising aperfluoropolyether base oil and a thickener. When the proportion isabove 40% by weight, the composition will be too hard to seal bearings,etc., whereas when the proportion is below 0.1% by weight, thethickening capacity of fluororesin will not be displayed, resulting inlowering of apparent viscosity and deterioration of dispersibility intothe base oil, and any satisfactory increase in the oil film formability,anti-scattering and anti-leakage property, and rust inhibitivenesscannot be expected. When the thickener is used in a proportion from alittle less than about 10% by weight on the basis of total weight of thethickener and the base oil, the composition takes a grease form. Whenthe thickener is used in a proportion of 5% by weight or less on thesame basis as above, the composition shows a fluidity in a category of“liquid grease”, as will be shown in the following Examples andComparative Examples, where the low-temperature characteristics areevaluated as a low-temperature viscosity of base oil mixtures, whereasin embodiments of using a thickener in a proportion of 30% by weight,the composition shows a semi-solid form in a category of grease, wherethe low-temperature characteristics are evaluated as a low-temperaturetorque.

Within such a range as not to injure the object of the invention, so farwell known fluorine-based additives can be used, if required, such asperfluoropolyether oils having terminals substituted with alcohols,carboxylic acids or their esters, amines, amides, phosphoric acids ortheir esters, phosphonic acid or its ester, reaction products, formedfrom isocyanates and alcohols or amines, etc.

The lubricant base oil can further contain additives so far added to theconventional lubricants such as various non-fluorine-based additives sofar having had no compatibility with perfluoropolyether oils, due to theaddition of fluororesin, a viscosity index-improver, a pour pointdepressant, an ashless dispersant, a metal-based detergent, anantioxidant, a rust inhibitor, a corrosion inhibitor, an antifoamingagent, an extreme pressure agent, an oiliness agent, afriction-controlling agent, a solid lubricant, etc., if required.

The antioxidant for use herein includes, for example, a phenol-basedantioxidant such as 2,6-di-t-butyl-4-methylphenol, 4,4-methylenebis(2,6-di-t-butylphenol), etc., and amine-based antioxidants such asalkyldiphenylamine having an alkyl group of 4-20 carbon atoms,triphenylamine, phenyl-α-naphthylamine, phenothiazine, alkylatedα-naphthylamine, phenithiazine, alkylated phenithiazine, etc.

The rust inhibitor for use herein includes, for example, fatty acid,fatty acid amines, alkylsulfonic acid metal salts, alkylsulfonic acidamine salts, oxidized paraffin, polyoxyethylene alkyl ethers, etc., andthe corrosion inhibitor includes, for example, benzotriazole,benzoimidazole, thiadiazole, etc.

The extreme pressure agent includes, for example, phosphorous-basedcompounds such as phosphoric acid esters, phosphorous acid esters,phosphoric acid ester amine salts, etc., sulfur-based compounds such assulfides, disulfides, etc., dialkyldithiophosphoric acid metal salts,dialkyldithiocarbamic acid metal salts, etc.

The oiliness agent includes, for example, fatty acids or their esters,higher alcohols, polyhydric alcohols or their esters, aliphatic amines,fatty acid monoglycerides, etc.

The solid lubricant includes, for example, graphite, molybdenumdisulfide, boron nitride, silane nitride, etc. In the case of usinggraphite or molybdenum disulfide as solid lubricant lowering of changesin heat resistance with time of perfluoropolyether base oil caneffectively prevent.

A composition to be formed by adding a thickener to a perfluoropolyetherbase oil can be prepared, for example, by any of the followingprocedures:

(a) By mixing a perfluoropolyether base oil with a thickener in apredetermined amounts, respectively, followed by thorough kneadingthereof through three rolls or a high pressure homogenizer, (b) byadding a perfluoropolyether oil and an aliphatic carboxylic acid to aheatable and stirrable reactor, melting the content with heating, andthen adding thereto a metal hydroxide (and an amide compound or analcohol compound) in predetermined amounts, to conduct metal saltingreaction (and amidation reaction or esterification reaction), followedby cooling and thorough kneading thereof through three rolls or a highpressure homogenizer, and (c) by adding a perfluoropolyether oil and anisocyanate to a heatable and stirrable reactor, heating the content,adding a predetermined amount of an amine thereto, followed theresulting reaction product by cooling and thorough kneading thereofthrough three rolls or a high pressure homogenizer.

EXAMPLES

The present invention will be described in detail below, referring toExamples, but is not limited thereto.

Example 1

The following three kinds of perfluoropolyether base oils were admixedwith 10% by weight of graphite powder (flake graphite powder CB-150, aproduct of Japan Graphite Co.; fixed carbon content: 98.0% or more, andaverage particle size: 40 μm), or molybdenum disulfide (LM13-SM powder,a product of Daito Lubricant Manufacturing Co.; average particle size:0.4 μm) on the basis of the sample, and 0.6 g each of the samples wassampled into individual glass dishes, 36 mm in diameter, smeared ontothe dish surfaces in a uniform thin film state, and left standing in athermostat tank at 200° C. to determine changes in percent oil weightloss with time.

The results are shown graphically in FIG. 1, where

-   -   : F(CF₂CF₂CF₂O)_(m)C₂F₅ (kinetic viscosity at 40° C.: 100        mm²/sec.)    -   ◯: +graphite    -   ▴: RfO[CF(CF₃)CF₂O]_(p)(CF₂CF₂O)_(q)Rf′ (kinetic viscosity at        140° C.: 180 mm²/sec.)    -   Δ: +graphite    -   ▪: RfO(CF₂CF₂O)_(m)(CF₂O)_(n)Rf′ (kinetic viscosity at 40° C.:        160 mm²/sec.)    -   : +graphite    -   ♦: +molybdenum disulfide

It can be seen from the results that in the case of perfluoropolyetherbase oils free from (CH₂O)_(n) groups as a repeat unit of polymer, thepercent oil weight loss at 200° C. is a substantially independent fromthe presence of graphite, whereas in the case of perfluoropolyether oilhaving (CH₂O)_(n) groups as a repeat unit of polymer, substantially allof the oil is evaporated and lost within a very short time by thepresence of graphite or molybdenum disulfide, particularly graphite.

Example 2

The following perfluoropolyether base oils (A) or (B) having variouskinetic viscosities at 40° C. were admixed with 10% by weight ofaluminum powder (a product of Wako Pure Chemical Co., purity: 99.5%, andparticle sizes: 53-150 μm) on the basis of the sample, and 0.3 ml eachof the samples was sampled into individual glass dishes, 37 mm indiameter, smeared onto the dish surfaces in a uniform thin film statesand left standing in a thermostat tank at 250° C. to determine weightsof entire glass dishes after 100 hours, thereby calculating percent oilweight losses.

Perfluoropolyether oil (A): F(CF₂CF₂CF₂O)_(m)C₂F₅

-   -   Kinetic viscosity at 40° C. (A-1) 65 mm²/sec.        -   (A-2) 100 mm²/sec.        -   (A-3) 200 mm²/sec.        -   (A-4) 23 mm²/sec.

Perfluoropolyether oil (B): RfO[CF(CF₃)CF₂O)_(p)Rf′

-   -   Kinetic viscosity at 40° C. (B-1) 180 mm²/sec.        -   (B-2) 400 mm²/sec.        -   (B-3) 25 mm²/sec.        -   (B-4) 1200 mm²/sec.

Perfluoropolyether oil (C): RfO(CF₂CF₂O)_(m)(CF₂O)_(n)Rf′

-   -   Kinetic viscosity at 40° C. 140 mm²/sec.

Emulsion-polymerized polytetrafluoroethylene powder (Mn: about 50,000 toabout 100,000; average primary particle size: 0.2 μm) was used asfluororesin powder.

The results are shown in the following Table 1, together with kinds andamounts (parts by weight) of base oils, amounts (parts by weight) offluororesin and additive, where the kinetic viscosity at 40° C. and pourpoint (according to JIS K2269, corresponding to ASTM D97) of the baseoil or base oil-fluororesin mixture, and percent weight loss andlow-temperature viscosity (kinetic viscosity at −40° C. according to JISK2283, corresponding to ASTM D445) are given as results ofdetermination, where Nos. 1-12 relate to Examples, whereas Nos. 13-15relate to Comparative Examples.

TABLE 1 Lubricating oil Items of determination (composition) KineticPercent Low- Fluoro viscosity weight Pour temperature Base oil resin at40° C. loss point viscosity No. Kind Amount Amount (mm²/sec.) (%) (° C.)(mm²/sec.) 1 A-1 100 — 65 41.3 <−60 8,800 2 A-2 100 1 100 27.7 <−6015,500 3 A-3 100 — 200 2.5 <−60 37,000 4 A-1 25 1 90 31.3 <−60 14,000A-2 75 5 A-1 40 3 130 16.9 <−60 25,000 A-3 60 6 A-2 30 — 162 10.7 <−6030,000 A-3 70 7 A-1 70 — 105 27.2 <−60 36,000 B-2 30 8 A-2 40 — 140 31.2−50.0 75,000 B-1 60 9 A-2 80 5 130 23.2 −55.0 45,000 B-2 20 10 A-3 50 3190 29.8 −50.0 80,000 B-1 50 11 B-2 100 — 400 34.2 −30 Impossible todetermine 12 B-4 100 — 1200 1.0 −15 >100,000 13 A-4 100 — 23 94.4 <−6030,000 14 B-3 100 3 25 98.3 −60.0 11,000 15 C 100 — 140 93.0 −60.0 4,000

It can be seen from the results that the percent weight loss at 250° C.is considerably increased in the cases of using base oils having akinetic viscosity at 40° C. of less than 50 mm²/sec. (Nos. 13 and 14),and the percent weight loss at 250° C. is considerably increased after100 hours in the case of using a base oil having (CF₂O)_(n) groups as arepeat unit of polymer (No. 15), so the sample has been almost lost,whereas the percent weight loss at such a high temperature as 250° C. iswithin an acceptable range in the cases of using base oil having akinetic viscosity at 40° C. in a range of 50-1,500 mm²/sec., and thebase oils having a kinetic viscosity at 40° C. in a range of 50-250mm²/sec. have the similar tendency even at a kinetic viscosity at −40°C. (Nos. 1-10).

Furthermore, in addition above items, grease consisting of 70 parts byweight of A-1 and 30 parts by weight of fluororesin (No. 21); 70 partsby weight of A-2 70 and 30 parts by weight of fluororesin (No. 22); 70parts by weight of B-2 and 30 parts by weight of fluororesin (No. 23);and 70 parts by weight of B-3 and 30 parts by weight of fluororesin (No.24) were subjected to a low-temperature torque test (according to JISK2220.5.14, torques were measured at the start-up and in the stationarystate; corresponding to ASTM D1478). The results are shown in thefollowing Table 2. No. 24 relates to Comparative Example.

TABLE 2 Items of determination No. 21 No. 22 No. 23 No. 24 Kineticviscosity at 40° C. (mm²/sec.) 65 100 400 25 Percent weight loss (%)29.1 20.3 15.8 69.4 Pour point (° C.) <−60 <−60 −30 −60.0Low-temperature viscosity (mm²/sec.) 8800 15500 X 11,000 Low-temperaturetorque At start-up (N · cm) 7.8 8.7 X 8.0 In stationary state (N · cm)3.8 4.5 X 4.1 Note) X: impossible to determine

1. A lubricant for use in contact with graphite or molybdenum disulfideor in contact with aluminum materials, which comprises aperfluoropolyether oil free from (CF₂O)_(n) groups as a repeat unit ofpolymer and having a kinetic viscosity at 40° C. of 50-1,500 mm²/sec, asa base oil.
 2. A lubricant according to claim 1, wherein theperfluoropolyether base oil has a kinetic viscosity at 40° C. of 50-250mm²/sec.
 3. A lubricant according to claim 1, wherein theperfluoropolyether base oil is at least one of perfluoropolyether oil(A) represented by the following general formula (A):F(CF₂CF₂CF₂O)_(m)C₂F₅ (where m is an integer of 2-100), andperfluoropolyether oil (B) represented by the following general formula:RfO[CF(CF₃)CF₂O]_(p)CF₂CF₂O)_(q)Rf′ (where Rf and Rf′ are same ordifferent perfluoroalkyl groups having 1-5 carbon atoms, p+q=2-200,q/p=0-2, and q can be zero, and CF(CF₃)CF₂O groups and CF₂CF₂O groupsare in random combination in the main chain).
 4. A lubricant accordingto claim 2, wherein the perfluoropolyether base oil is at least one ofperfluoropolyether oil (A), represented by the following generalformula:F(CF₂CF₂CF₂O)_(m)C₂F₅ (where m is an integer of 2-100), andperfluoropolyether oil (B) represented by the following general formula(B):RfO[CF(CF₃)CF₂O]_(p)(CF₂CF₂O)_(q)Rf′ (where Rf and Rf′ are same ordifferent perfluoroalkyl groups having 1-5 carbon atoms, p+q=2-200,q/p=0-2, and q can be zero, and CF(CF₃)CF₂O groups and CF₂CF₂O groupsare in random combination in the main chain).
 5. A lubricant accordingto claim 1, wherein the lubricant is a lubricating oil.
 6. A lubricantaccording to claim 2, wherein the lubricant is a lubricating oil.
 7. Alubricant according to claim 1, wherein a thickener is furthercontained, and the lubricant is used as a grease.
 8. A lubricantaccording to claim 7, wherein the thickener is fluororesin powder.
 9. Alubricant according to claim 2, wherein a thickener is furthercontained, and the lubricant is used as a grease.
 10. A lubricantaccording to claim 9, wherein the thickener is fluororesin powder.
 11. Alubricant according to claim 1, for use as impregnated in a sintered,oil-impregnated bearing containing graphite or molybdenum disulfide as asintering component.
 12. A lubricant according to claim 2, for use asimpregnated in a sintered, oil-impregnated bearing containing graphiteor molybdenum disulfide as a sintering component.
 13. A lubricantaccording to claim 1, for use in contact with metallic parts containinggraphite or molybdenum disulfide.
 14. A lubricant according to claim 2,for use in contact with metallic parts containing graphite or molybdenumdisulfide.
 15. A lubricant according to claim 1, for use in atmosphereswhere graphite or molybdenum disulfide prevails as scattered particlesor contaminants.
 16. A lubricant according to claim 2, for use inatmospheres where graphite or molybdenum disulfide prevails as scatteredparticles or contaminants.
 17. A lubricant according to claim 1, for usein contact with aluminum materials as a sliding member.
 18. A lubricantaccording to claim 2, for use in contact with aluminum materials as asliding member.